In the manufacture of an electronic device such as a semiconductor device, a plasma processing is performed on a processing target object by using a plasma processing apparatus. In general, the plasma processing apparatus includes a processing vessel, a gas supply system, a first electrode, a second electrode and a high frequency power supply. The gas supply system is configured to supply a processing gas into the processing vessel. The first electrode and the second electrode are disposed with a space within the processing vessel therebetween. The high frequency power supply is configured to supply a high frequency power to either one of the first electrode and the second electrode. Generally, in the plasma processing performed in this plasma processing apparatus, the processing gas is supplied into the processing vessel from the gas supply system, and the high frequency power from the high frequency power supply is supplied to either one of the first electrode and the second electrode.
There may be a plasma processing in which two separate stages of generating plasma of different processing gases are performed alternately. In this kind of plasma processing, when transitioning from a preceding stage to a succeeding stage, the processing gas supplied from the gas supply system is changed, and a setting of the high frequency power is changed.
Since a gas has a mass, there is required a time period from a time point when the processing gas supplied from the gas supply system is changed to a time point when the processing gas within the processing vessel is actually changed. Meanwhile, the high frequency power whose setting has been changed is supplied to either one of the electrodes nearly without delay. Accordingly, it happens that the high frequency power whose setting has been changed is supplied to either one of the electrodes before the processing gas within the processing vessel is changed.
As a resolution, there is proposed a technique in which a supply of the high frequency power to the electrode is begun after it is confirmed from a detection result of an emission spectrum within the processing vessel that a processing gas for a succeeding stage has reached the processing vessel. This technique is described in Patent Document 1.
Patent Document 1: Japanese Patent Laid-open Publication No. 2013-058749
However, there may be no detectable difference between an emission spectrum of plasma of a processing gas used in a preceding stage and an emission spectrum of plasma of a processing gas used in a succeeding stage. In such a case, it may be difficult to accurately detect a time point when the processing gas is changed within the processing vessel. As a result, the setting of the high frequency power cannot be changed at an appropriate timing.
Further, the plasma processing apparatus may be additionally equipped with a DC power supply connected to the first electrode. The DC power supply is configured to apply a negative DC voltage to the first electrode. In a plasma processing using this plasma processing apparatus, a level of the DC voltage output from the DC power supply may be changed when transitioning from a preceding stage to a succeeding stage. In this plasma processing as well, the level of the DC voltage may not be changed at an appropriate timing.
Thus, in a plasma processing method of sequentially performing multiple cycles, each of which includes plural stages which generate plasma of different processing gases within the processing vessel and which are performed in sequence, it is required to change the setting of the high frequency power and/or the setting of the level of the DC voltage at appropriate timings after transitioning from the preceding stage to the succeeding stage.